1. Field of the Invention
The present invention relates to the field of oil production via artificial lift methods, and more particularly, to systems for sensing the pressure adjacent the intake of the artificial lift mechanism.
2. Prior Art
A typical artificial lift oil well will have a pump located at a suitable depth in the well, often adjacent the bottom thereof, to deliver oil through pipe within the well casing to the surface. These pumps are designed to operate beneath the oil level in the well and will be subject to rapid deterioration and premature failure if allowed to operate with too low a fluid level or pressure at the pump intake. Accordingly, for a given pump there is a minimum oil level above the intake which will minimize wear or damage and prolong operation thereof; one important class of these pumps, known as submersibles being subject to cavitation and quick burn out of its submerged driving motor if the fluid level falls below such minimum.
In typical oil wells production is achieved by the seepage of oil from an oil-bearing geological formation or reservoir to the unbalance between the pressure existing in the reservoir and that due to fluid level in the well itself. Accordingly, the well production decreases with increasing oil level in the well. Thus, the oil level should be maintained within predetermined limits, a higher level unnecessarily reducing the well production and a lower level increasing the frequency of pump failure and thereby increasing costs because of the time and expense incurred in repairing a pump. These costs and down time are substantial, since the pump must be brought to the surface for repairs or replacement and relowered before the well may be started up again.
For a properly designed pump, rapid deterioration and failure may be prevented with a relatively low intake pressure, which by way of example, may represent less than 5 percent of the static level (e.g. the non-pumping equilibrium level) of the well. Also, typically production rates begin diminishing immediately with an increase in oil level in the well so that it is desirable to maintain the oil level within a few per cent of the minimum allowed level. On the other hand, there will be a few times when the pump will not be producing, such as during pump failure, removal and replacement, etc. At this time, the oil level in the well will reach or at least approach its maximum or static level which typically may be on the order of 20 times the normal level. Accordingly, any sensing system for sensing oil levels within the normal (desired) range must be capable of very substantial over pressures without altering the performance thereof.